1. Field of the Invention
The present invention relates to the construction of an MIM or MIS electron source (hereinafter referred to as an MIM/MIS electron source) and to a method of manufacturing an MIM/MIS source, and more particularly it relates to the construction and method of manufacturing an MIM/MIS electron source that emits a desired electron distribution and emits electrons uniformly.
2. Background of the Invention
An MIM(metal-insulator-metal)/MIS (metal-insulator-semiconductor) electron source is a surface emission type of electron source having a three-layer structure, in which an insulating layer is sandwiched by either a metal or a semiconductor. It enables the achievement of a uniform emission of electrons over a large surface area and, because this electron source is highly immune to surface impurities, it is expected to be suitable for such applications as electron beam writing apparatuses and displays. FIG. 7 illustrates the principle of this electron source. By applying a voltage across the metal or semiconductor 602 and 603 which sandwiches the insulating layer 601, electrons 608 are Fowler-Nordheim tunneled through the insulation forbidden band 604 (tunnel effect) and electric field that occurs within the insulation conduction band 605 causing electron to accelerate and move thereof from the metal or semiconductor 602, which has a high electron potential, toward the metal 603, which has a low electron potential. Part of these electrons pass through the semiconductor 603 and are emitted into the vacuum 606.
In the past, various materials have been used in the above to the present in wide-ranging research. For example, an Al--Al.sub.2 O.sub.3 --Au structure is shown on page 568 of Vol. 32 Issue 8 (1963) of Applied Physics, and a Si--SiO.sub.2 --Al structure and an nSi--SiO.sub.2 -nonSi-nSi structure is indicated on page 2096 of Issue B14 (1996) of Journal of Vacuum Science and Technology.
In addition to the two above-noted citings, there is also an indication of the shape of a three-layer structure, on page 359 of Electronic Engineering 11 (1990), and on page 801 of Issue B12 (1994) Of Journal of Vacuum Science and Technology. In particular, a structure for achieving a desired beam cross-sectional shape which is shown in FIG. 8, is indicated on page 359 of Electronic Engineering 11 (1990), and on page 2201 of Issue B13 (1995) Of Journal of Vacuum Science and Technology.
In FIG. 8, the reference numeral 702 denotes a first conductive layer, 701 is an insulating layer that is formed on the first conductive layer 702, and 703 is a second conductive layer that is formed on the insulating layer 701. In this MIM/MIS electron source, the structure is such that only electrons 708 from thin part of the intermediate insulating layer 701 are allowed to be released. In the Japanese Unexamined Patent Publication (KOKAI) H8-315722, there is disclosure of an example of forming the above-noted three-layer structure microscopically using minute particles.
However, in the above-noted prior art, because of a step that exists in the metal or semiconductor layer which forms the edge of the beam, the change in the film thickness changes the shape of the beam edge, thereby making it difficult to achieve the desired pattern shape.
In the example in the Japanese Unexamined Patent Publication H8-315722, in which minute particles are used, because of the difficulty in achieving a uniform disposition of two types of particles, and because the three-layer structure is microscopically oriented in all directions, electrons are emitted in all directions, the result being that it is difficult to achieve a uniform electron emission of a desired beam shape.